A barbell and weight plates are very common and well known pieces of equipment for weight lifting exercises. A barbell commonly has a shaft with a central section suited for a user to grasp during use of the equipment and two terminal sections, one at either end of the barbell, suited for bearing and retaining weight plates. Weight plates are commonly cylindrical (for safety, aesthetic, weight distribution, and mass centering purposes, among others) with a hole through the center. The hole is sized to facilitate the placement of matching weight plates on each of the terminal sections of the barbell.
Different quantities of weight are required or desirable for different users and for different exercises with a barbell, for instance when exercising different muscle groups. Barbells and weight plates are commonplace in any professional gym or home gym and are most often used by a plurality of users with different weight requirements. It is important that weight plates be easy to mount on and remove from the terminal sections of barbells so that different combinations of weight plates can be used to achieve different total quantities of weight customized to each particular user for each particular exercise.
It is furthermore important that the weight plates be completely fixed relative to the barbell during use. At a minimum, this involves the weight plates sufficiently resisting movement (i.e., sliding) in either axial direction with respect to the bar or shaft. This is necessary to prevent the weights from unintentionally changing position along the bar or possibly slipping off the bar altogether. Changing position along the bar and slipping off the bar would change the balance and loading characteristics of the weighted bar and thereby present a potential risk of harming the user as well as the user's surroundings, possibly including property, floor surfacing, other weight equipment, persons, pets, plants, or anything else in the user's vicinity. It is therefore important to have a means of securely fixing a weight on the barbell in order to prevent it unintentionally slipping.
Fixing the relative position of a weight with respect to a barbell is traditionally achieved by securing the weight on both sides and thus preventing movement in both axial directions. Each side of a weight is traditionally held fixed relative to the barbell by one of three possible arrangements. A weight added to an otherwise unloaded terminal section of a barbell is usually mounted on the bar until abutment with a stopper. This stopper, sometimes a part of the barbell itself, is by design intended to eliminate movement in one axial direction of the first weight. If a second weight is added, the second weight is slid onto the bar until a face of the second weight abuts with the opposing face of the first weight. The first weight becomes “sandwiched” between the stopper and the second weight. Each successive weight added completes a “sandwich” on the weight which precedes it. The final weight mounted is most often followed by a collar, the collar possessing a means to lock and unlock to the barbell.
Many locking collars for a bar or shaft are well known in the art. A large number use some variation of a bolting mechanism, whereby tightening a radial bolt within the collar drives the bearing surface of the bolt against the bar to create a compressive force. The resulting forces within the bolt-collar-bar system provides resistance to changes in the relative position of the collar with respect to the bar while the bolt remains tightened. One significant limitation of bolt devices is the time and inconvenience involved in turning the bolt successive times to both lock and unlock the collar. It is furthermore unclear to the user when the bolt is “tight enough,” resulting in many users over-tightening the bolt and risking damage to the bar and making un-tightening difficult.
Locking collars such as those disclosed in U.S. Pat. Nos. 4,893,810 and 6,007,268 use different implementations of metal balls which are contained between a coaxial inner collar and outer collar. A spring which bears upon a flange at either end of the spring provides a biasing force to provide a constant relative position of the inner collar with respect to the outer collar. In an isolated state (without external forces being imposed by a user), the metal balls partially protrude into the collar's central cylindrical cavity. This provides radial bearing on the bar which, like the bolt described above, holds the collar against the bar to limit the collar's ability to slide along the bar.
When a user changes the axial position of the inner collar relative to the other collar—either by pulling them apart, as is done in U.S. Pat. Nos. 4,893,810 and 6,007,268, or by pushing the collars together, as is done in U.S. Pat. No. 5,295,934—the balls are freed to move radially and therefore do not necessarily protrude into the collar's central cavity. While in this temporary unlocked state the collar can be freely slid along the bar. When the user stops applying a compressive or tensile force to the device, the collar returns to its original locked conformation. Locking collars of this type have the limitation that a user must apply a constant compressive or tensile force while adjusting the position of the collar along the bar.
A considerable limitation of any of the above described collars known in the art is the dependence on the elimination of gaps between stacked weights in order to achieve effective use. When small gaps are present, a collar lock prevents weights from sliding off the barbell but does nothing to prevent them axially sliding small amounts during use. This presents the danger of changing the bar's balance and loading characteristics while in use, which can, for instance, increase the risk of the user accidently dropping the barbell to one side. When large gaps are present, it is possible that a sliding weight could gain sufficient momentum to overcome the resistive forces of the collar upon impact with the collar and result in the collar and weight sliding off the barbell during use. In short, collars up this point have only offered limiting axial movement of a weight on a bar in one direction.